Amphiphilic materials spread at the air/water interface have been the subject of intensive study over a long period. Langmuir-Blodgett (LB) trough systems include areas that contain a liquid support subphase (e.g. water) and movable barriers that enclose the surface of the support liquid phase on which monomolecular layers of suitable substances (e.g. substances having amphiphilic molecules) can be produced. The structure and physical properties of such layers can be controlled by changing the surface area enclosed by the movable barriers.
Once a monomolecular layer (also called monolayer) having a preferred structure is produced on the surface of the subphase liquid, the monolayer can be transferred onto solid substrates, in which form they are often referred to as Langmuir-Blodgett (LB) films. The monomolecular layers are prepared by depositing a small quantity of a solution of the substance onto the surface of the subphase liquid and allowing the solvent to evaporate leaving molecules of the solute spread discontinuously over the surface of the subphase liquid. The molecules of the solute are then drawn together by reducing the surface of the subphase liquid upon which the molecules are spread, using movable barriers, until the desired monolayer is obtained. The formation of the monolayer can be detected by monitoring the surface pressure using an electronic micro balance, where a sharp rise in pressure indicates that a continuous monolayer has been achieved.
The isotherm of a film at the surface of the subphase liquid is a plot of the film's surface pressure versus surface area. The isotherm measurement technique has been widely used to characterize the property of molecules, typically nanomaterials and biomolecules which are very expensive. Different molecules have different sizes and different interactions between them, and the barriers cannot move too close to avoid disturbing a sensor plate or sensor wire between the barriers, so that the configuration of the trough width (W) versus trough length (L) should be optimized in size (W×L) and profile (W/L) to be able to measure the full isotherm using a minimal amount of the expensive substances. To solve the problem, different sized troughs with different configurations have been made to adapt to different substances for different applications. This approach makes it expensive, difficult and time consuming to switch troughs for different applications.